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I am trying to get the acceleration on the two axes which are perpendicular to the direction of the gravity irrespective of the orientation of the phone, but not quite sure on how to do that,

I have been looking into using TYPE_MAGNETIC_FIELD and TYPE_ROTATION_VECTOR but could not figure out on how to achieve the same.

I just need the acceleration in the xy plane assuming the direction of the gravity is in the z plane, irrespective of the phone orientation.

Thanks in Advance

Gaurav Singh
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1 Answers1

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That's not simple :)

to use the TYPE_MAGNETIC_FIELD you should know how the earth magnetic field is oriented at your location and it's not trivial.

You can try to use the TYPE_GRAVITY and TYPE_LINEAR_ACCELERATION: the first returns the gravity acceleration vector, the second the acceleration of the device excluding gravity (it should be something like LINEAR_ACCELERATION = ACCELEROMETER - GRAVITY, but i don't know how precise it is).

To have the gravity on the z axis you have to perform a rotation of the gravity vector to have it in the form (0 0 g)... Actually you have to find the rotation matrix that tranform your gravity vector in the form (0 0 g). More on this here (wikipedia).

Once you have this matrix you apply it to the linear acceleration vector and its x and y components will be the ones you are looking for.

If your phone doesn't have this two sensors, you have to calculate gravity and linear acceleration yourself: to do this you can implement an hig-pass filter to get the linear acceleration and a low pass filter to get the gravity vector. More on this here.

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